2What are network devices??? Computer networking devices are units that mediate data in a computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS)or Interworking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment.
3Functions of network devices Separating (connecting) networks or expanding networke.g. repeaters, hubs, bridges, routers, switches, gatewaysRemote accesse.g. 56K Modems and ADSL modems
4Expanding NetworkNetworks cannot be made larger by simply adding new computers and more cablesLess efficient !!Can install components tosegment (divide) large LAN to form smaller LANsconnect LANsRequired componentsRepeaters, bridges, routers, switches or gateways
5Types of network devices ModemRJ-45Ethernet cardHubSwitchRepeaterBridgeRouterGateway
6MODEM :A MODEM is a computer peripheral that allows you to connect and communicate eith other computers via telephone lines.
7MODEM stands for modulation and demodulation. Allow computers to communicate over a telephone lineEnable communication between networks or connecting to the world beyond the LAN
8Cannot send digital signal directly to telephone line Sending end: MODulate the computer’s digital signal into analog signal and transmitsReceiving end: DEModulate the analog signal back into digital form
9Types of modems 1.Internal modems: 2. EXTERNAL MODEMS: The modems that are fixed within the computer.2. EXTERNAL MODEMS:The modems that are connected externally to the computer.
10Working of a modemMODEM converts digital signals to A/F (Audio Frequency) tones which are in the frequency range that the telephone lines can transmit and also it can convert transmitted tones back to digital information.
11RJ-45RJ 45 is the short for Registered jack 45. RJ 45 is an eight wire connector, which is commonly used to connect computers on the local area networks i.e., LAN’s especially Ethernets. (Ethernet is a LAN architechture developed by Xerox Corp along with DEC and Intel. It uses either bus or star topologyand suports data transfer rates upto 10 Mbps.)
12RJ-45 jack.Inserting an RJ-45 connector into its jack.
13Ethernet cardEthernet is a LAN architecture developed by Xerox corp. in association with DEC and Intel. Ethernet uses either bus or star topology and supports data transfer rates up to 10 mbps.The computers that are part of Ethernet, have to install a special card called Ethernet card .
14An Ethernet card contains connections for either coaxial or twisted pair cables or both. Inserting Ethernet card in its slot on motherboard
15HUB Hub can be defined as one common point for connecting all the network devices.Various LAN segments areconnected to hub in order toorganize the working of thenetwork. A network hub connects the variousports of the optic fiber cable and helpsestablish a single network connection orsegment.
16How a hub worksThe most common operation it performs is that it repeats all the information it receives and forward it to all PC terminals attached to it.This repetition of dataresults in unnecessarydata traffic being sent tothe network. Therefore the data is sent in bulk without the identification of its destination.
17Limitations and Features Cannot link unlike segmentsCannot join segments with different access methods (e.g. CSMA/CD and token passing)Do not isolate and filter packetsCan connect different types of mediaThe most economic way of expanding networks
18SWITCH A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.
19Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub.Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately.By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub.
20FunctioningA switch is a telecommunication device which receives a message from any device connected to it and then transmits the message only to the device for which the message was meant. This makes the switch a more intelligent device than a hub (which receives a message and then transmits it to all the other devices on its network). The network switch plays an integral part in most modern Ethernet LANs.
21Advantages of Switches Switches divide a network into several isolated channels (or collision domains)Reduce the possibility of collisionCollision only occurs when two devices try to get access to one channelCan be solved by buffering one of them for later accessEach channel has its own network capacitySuitable for real-time applications, e.g. video conferencingSince isolated, hence secureData will only go to the destination, but not others
22Limitations of Switches Although contains buffers to accommodate bursts of traffic, can become overwhelmed by heavy trafficDevice cannot detect collision when buffer fullCSMA/CD scheme will not work since the data channels are isolated, not the case as in EthernetSome higher level protocols do not detect errorE.g. UDPThose data packets are continuously pumped to the switch and introduce more problems
23REPEATERA repeater is an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.
24In digital communication systems, a repeater is a device that receives a digital signal on an electromagnetic or optical transmission medium and regenerates the signal along the next leg of the medium. In electromagnetic media, repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance.Repeaters remove the unwanted noise in an incoming signal. Unlike an analog signal, the original digital signal, even if weak or distorted, can be clearly perceived and restored. With analog transmission, signals are restrengthened with amplifiers which unfortunately also amplify noise as well as information.
25BRIDGE Has one input and one output Used to isolate network traffic and computersHas the intelligent to examine incoming packet source and destination addresses.But cannot interpret higher-level informationHence cannot filter packet according to its protocol
26How bridges workBridges work at the Media Access Control Sub- layer of the OSI model.Routing table is built to record the segment no. of address.If destination address is in the same segment as the source address, stop transmit.Otherwise, forward to the other segment.
28ROUTERIn a common configuration, routers are used to create larger networks by joining two network segments.A router can be a dedicated hardware device or a computer system with more than one network interface and the appropriate routing software. All modern network operating systems include the functionality to act as a router.Routers will normally create, add, or divide on the Network Layer as they are normally IP-based devices.
29How a router functionsAs packets are passed from routers to routers, Data Link layer source and destination addresses are stripped off and then recreatedEnables a router to route a packet from a TCP/IP Ethernet network to a TCP/IP token ring networkOnly packets with known network addresses will be passed - hence reduce trafficRouters can listen to a network and identify its busiest partWill select the most cost effective path for transmitting packets
30Distinguishing Between Bridges and Routers Bridges forward everything they don’t recognizeRouters select the best pathRouters are layer 3 devices which recognize network addressBridges are layer 2 devices which look at the MAC sublayer node address
31GATEWAYSAny device that translates one data format to another is called a gateway.A gateway is a network device that connects dissimilar networks. It establishes an intelligent connection between a local network and external networks with completely. different structures.
32Some examples of gateways include a router that translates data from one network protocol to another, a bridge that converts between two networking systems, and a software application that converts between two dissimilar formats.The key point about a gateway is that only the data format is translated, not the data itself. In many cases, the gateway functionality is incorporated into another device.The gateway often acts as a proxy server and a firewall.